This dissertation aims to contribute to a socio-informatics approach by addressing sustainable everyday mobilities through practice-based design. Supporting the sustainable transformation of everyday mobilities is a rising demand of our times that can profit highly from mobile sustainable interaction design (SID). However, conventional designs to support sustainable mobilities have often been criticized as too rationalistic and normative, ignoring the complex nature of mobility patterns. In particular, design interventions that only address a very specific mobility mode are often revealed to be insulated solutions that do not account how for their further embeddedness in everyday mobility practices. These shortcomings can either be or have problematic unintended consequences, such as rebound effects (Shove 2010; Banister and Button 2015). To address these issues, I studied SID for sustainable mobilities in real-life settings using a socio-informatic approach. In particular, this thesis examines how SID can be applied to focus on everyday mobilities as habituated practices. Thus, it aims to answer the following question: "How should a practice-based design approach be applied to support sustainable everyday mobilities in everyday life settings?" The research question is examined through the lens of three research fields: first transport information systems (TIS), second shared mobility services (SMS) and third eco-feedback tools (EFT). Therefore, six research studies were completed to study and support the environmental and social sustainability of everyday mobility practices. The studies showed that a practice-based approach addresses SID for everyday mobilities on three levels: first, by elaborating a new methodological understanding to study everyday mobilities as evolving practices; second, by evolving methods and tools that are able to reflect on the development of new mobility practices in real-life contexts; and third, by supporting SID that goes beyond the normative stance but is built upon the practices of everyday life mobilities in the research fields of TIS, SMS and EFT.